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Bonsall Tonalite
Field Collector: Esper Signius Larsen Jr.
Place Collected:Near San Luis Rey Mission, San Luis Rey Quadrangle, CA
Object number: ROC21697
DescriptionPlutonic, medium-grained (1-5 mm) igneous rock that is salt and pepper on a fresh surface, with suspicious biotite layers (1-2 cm thick) that doesn't appear to be foliation. Analyzed mineral modes by Larsen (1948) are 50% plagioclase, 25% quartz, 14% biotite, 6% hornblende, 4% alkalic (K-feldspar), and 1% accessory minerals. The plagioclase is light grey and ≤ 5 mm across, quartz is light-grey and ~1-2 mm, biotite is black and ≤ 2 mm, horblende is black and ~1 mm, and K-fledspar is indistinguishable in hand specimen.
In Collection(s)